Our invention comprises improvements in the invention described in co-pending patent application Ser. No. 229,405, filed Aug. 8, 1988 by William J. Fuhrman, one of the co-inventors of this invention. The invention of the earlier application of William J. Fuhrman comprises a method for forming internal teeth for a ring gear by advancing an annular workpiece across external die teeth of a floating mandrel that is surrounded by a die ring.
The workpiece of the Fuhrman invention is extruded through the die teeth by a punch that is actuated by a ram, the punch entering the annular space between the mandrel and the die ring. As the punch is advanced, the workpiece is extruded throughout a major portion of its axial length. The punch then is withdrawn to permit entry of a second workpiece in registry with the first workpiece in end-to-end relationship. The second workpiece is received over a pilot portion of the mandrel. Subsequent movement of the punch advances the second workpiece, which in turn advances the partially extruded workpiece until the latter is fully extruded and moved beyond the location of the external die teeth of the mandrel.
During the extrusion of a workpiece using the process of the invention of the co-pending application of William J. Fuhrman relatively large friction forces occur because of the necessity of the workpiece, during the extrusion process, to slide along the annular inner surface of the die ring. If the workpiece is made of steel--for example, SAE 5130 steel--a relatively large and costly extrusion press is required. This is due partly to the high friction forces that are established during the extrusion process. In a typical embodiment the extrusion forces may be 240 tons or more.
In the extrusion process of the invention of the co-pending William J. Fuhrman application as well as in the present invention, the workpiece is caused to enter the entrance portion of the die teeth of the mandrel as the extrusion of metal begins. The entry of the workpiece is facilitated by a ramp portion on the leading edge of the die teeth adjacent to the pilot portion of the mandrel. The actual internal tooth formation region of the external teeth is only a fraction of the total die tooth length of the mandrel teeth. The trailing edge portions of the teeth are recessed to provide a progressively decreasing outer diameter. They also are formed with a progressively decreasing tooth thickness. This permits the die teeth of the mandrel to guide the workpiece during the extrusion process, but it avoids excessive friction forces between the teeth of the mandrel and the metal that is being extruded on the inside diameter region of the workpiece.
In our improved invention we have reduced substantially the friction forces that are required during the extrusion process. We have done this by making provision for movement of the die ring in unison or synchronism with the movement of the workpiece as the latter is extruded through the die teeth. After the die teeth fully extrude the internal teeth of the workpiece, the workpiece that is inserted in end-to-end relationship with respect to the extruded workpiece as well as the mandrel are raised by pneumatic cylinder rods without any relative motion occuring between the workpiece and the die ring. As the ring, the mandrel and the workpiece are raised, the extruded workpiece is stripped and ejected from the press. As the mandrel, the die ring and the partially extruded workpiece then are returned to a lower level, a subsequent workpiece can be inserted above the mandrel pilot portion and the foregoing method steps are repeated in the same sequence.